This invention relates to a housing of a rotary fluid pump, and more particularly, to a rotor housing of a rotary fluid pump having a plurality of vanes made of carbon.
Conventional rotor housings are made of cast iron, or is formed with chromium plating on the inner peripheral surface thereof, while the vanes adapted to slidingly contact the inner peripheral surface of the rotor housing are generally made of carbon in light of wear resistance and self-lubrication properties. However, the coefficient of friction defined between carbon and cast iron, or carbon and chromium is relatively large such as 0.15 and 0.16, respectively. This results in the vanes tending to be extremly worn that deteriorates sealability between vanes and the rotor housing. Generally, this condition reduces service life of the pump.
In order to overcome this drawback, a rotor housing made of aluminum or aluminum alloy has been proposed to allow sliding contact with the vanes made of carbon to thus provide a small coefficient of friction of 0.06 between aluminum (aluminum alloy) and carbon to reduce the amount of wear of the carbon vanes. However, since thermal expansion of aluminum is large, such a rotor housing may tend to expand along the axial direction thereof due to heat generation caused by the frictional contact between the housing and the vanes. This creates and increases disadvantageously the clearance between the side faces of the rotor and side surfaces of side housing to thereby deteriorate sealability therebetween.